1. Field of the Invention
The invention relates to a method for applying a scale to a carrier, in particular to an optical element of an objective as carrier, more particular to a lens.
The invention also relates to an objective for semiconductor lithography, a scale with a measuring graduation being applied to a lens or an inner holder.
When carrying out changes in position of an optical element in an objective, e.g. on the lens which is mounted in an inner holder and which is connected to an outer holder via corresponding intermediate elements, it is advantageous to determine the position of the change in position of the optical element when this experiences a corresponding offset, e.g. through the use of manipulators.
2. Description of the Related Art
It is known to arrange on one of the two holder parts, preferably the inner holder, a separate glass carrier which is provided with a scale with an etched-in measuring graduation. In this case, the glass carrier is connected to the underlying holder, which is generally composed of steel, via fixing elements. Besides the disadvantage of an additional component and an associated higher fixing outlay, a further disadvantage of the known measuring method resides in different thermal expansions between the glass carrier with the scale and the holder on which the glass carrier with the scale is arranged. As a result of the different thermal expansions between the two parts, there is the risk of the measurement result becoming more inaccurate.
Therefore, the present invention is based on the object of providing a method for applying a scale to a carrier and an apparatus therefore which can be used to carry out measurements with simple means, with the possibility, in particular, of effecting measurement with higher accuracy and with relatively simple means, in the case of an offset of an optical element.
According to the invention, this object is achieved by means of a method for applying a scale to a carrier, a material layer being applied to said carrier in such a way that changes in length of the material layer on account of temperature changes correspond at least approximately to changes in length of said carrier on account of temperature changes, and said scale being introduced into or applied to said material layer with a measuring graduation.
More specifically, this object is achieved by means of a method for applying a scale to an optical element of an objective for semiconductor lithography, a material layer being applied to an optical element in such a way that changes in length of said material layer on account of temperature changes correspond at least approximately to changes in length of said optical element on account of temperature changes, and said scale being introduced into or applied to said material layer with a measuring graduation.
This object is also achieved in an objective for semiconductor lithography, wherein a scale being provided on an inner holder or on a lens.
By virtue of the fact that a material layer is applied directly to the carrier, e.g. to an optical element of an objective, such as e.g. an objective for semiconductor lithography, the thermal expansion profile of the carrier being forced on the thermal expansion profile of said material layer, on the one hand separate fixing elements for the scale are avoided and on the other hand problems with a varying thermal expansion coefficient no longer arise. This means that the position and changes in position of the carrier, e.g. a lens, can be ascertained with significantly higher accuracy.
In a highly advantageous improvement of the invention, it may be provided that the scale is introduced directly into the carrier, e.g. the holder of a lens, or else is introduced into or applied to the lens itself in an optically inactive region, i.e. into a region which is not required for the exposure.
In a further embodiment of the invention, it may be provided that the material layer for the scale has at least approximately the same thermal expansion coefficient as the carrier. If e.g. a lens is provided as the carrier, then the material layer for the scale may be composed of the same material as the lens. Identical thermal expansion coefficients are thus present in this case. The same material layer also results automatically when the scale is introduced directly into the lens itself, e.g. through corresponding etching-in or scribing-in.
In a highly advantageous further improvement of the invention, it may be provided that glass is used as the material layer, the measuring graduation of the scale being applied to the glass layer. In this case, the measuring graduation of the scale may be vapor-deposited onto the glass layer.
The application of the material layer to the carrier, e.g. a lens or the holder of a lens, may be effected by sputtering or vapor deposition.
If the scale is arranged on the lens or on the inner holder of the lens, then corresponding measuring elements for measurement, e.g. a sensor, which measures the position and the displacement distances of the lens by means of the measuring graduation of the scale will be provided on the associated outer holder or in a corresponding region of the objective.
A possible sensor is e.g. an incremental capacitive or incremental inductive sensor, an interferometric transmitter or else another sensor which operates with the desired high measurement accuracy, which should lie in the nanometers range.
Advantageous developments and improvements emerge from the rest of the subclaims and from the exemplary embodiments, whose principles are described below with reference to the drawing.